It is crucial that the temperature or the like of a substrate processed by, for instance, a substrate processing apparatus, such as a semiconductor wafer (hereafter may be simply referred to as a “wafer”) be measured with a high degree of accuracy in order to accurately control the shapes, the physical characteristics and the like of films, holes and the like formed on the wafer by executing various types of processing such as film formation and etching. Accordingly, various wafer temperature measuring methods have been proposed in the related art, including the use of a resistance thermometer and the use of a fluorescence thermometer that measures the temperature at the rear surface of the base material.
In recent years, research into temperature measuring methods and temperature measuring apparatuses that enable direct measurement of the wafer temperature, which is difficult with the temperature measuring methods in the related art, has gained significant ground (see, for instance, International Publication No. 03/087744). A specific example of a temperature measuring apparatus is now explained in reference to FIGS. 19 and 20. FIG. 19 illustrates the principle of a temperature measuring apparatus in the related art, whereas FIG. 20 is a conceptual diagram of interference waveforms measured with the temperature measuring apparatus.
The temperature measuring apparatus 10 in FIG. 19 is constituted with a low coherence interferometer that may be achieved by adopting the basic principle of, for instance, a Michelson interferometer. The temperature measuring apparatus 10 includes a light source 12 constituted with, for instance, an SLD (super luminescent diode) having low coherence characteristics, a beam splitter 14 that splits the light originating from the light source 12 into two beams, i.e., reference light to be radiated onto a reference mirror 20 and measurement light to be radiated onto a measurement target 30, the reference mirror 20 drivable along a single direction, with which the optical path length of the reference light can be varied, and a light receiver 16 that receives the reference light reflected at the reference mirror 20 and the measurement light reflected at the measurement target 30 and measures the extent of interference.
In this temperature measuring apparatus 10, the light originating from the light source 12 is split at the beam splitter 14 into two beams, i.e., the reference light and the measurement light. The measurement light is radiated toward the measurement target and is reflected at various layers, whereas the reference light is radiated toward the reference mirror 20 and is reflected at the mirror surface. Then, both the reflected reference light and the reflected measurement light reenter the beam splitter 14, and depending upon the optical path length of the reference light, the reflected light beams become superimposed upon each other, thereby inducing interference. The resulting interference wave is detected by the light receiver 16.
Accordingly, the reference mirror 20 is driven along the single direction to alter the optical path length of the radiated light for the temperature measurement. Since the coherence length of the light from the light source 12 is small due to the low coherence characteristics of the light source 12, intense interference manifests at a position at which the optical path length of the measurement light and the optical path length of the reference light match and the extent of interference is substantially reduced at other positions under normal circumstances. As the reference mirror 20 is driven along, for instance, the forward/backward direction (the direction indicated by the arrows in FIG. 19) and the optical path length of the reference light is adjusted as described above, the reflected measurement beams from the individual layers (A layer and B layer) at the measurement target with different refractive indices (n1, n2), and the reflected reference light interfere with each other and, as a result, interference waveforms such as those shown in FIG. 20 are detected. Thus, the measurement of the temperature at the measurement target along the depthwise direction is enabled.
As the temperature of the measurement target being heated with a heater or the like changes as shown in FIG. 20, the measurement target expands. At this time, the refractive indices at the various layers at the measurement target 30, too, become altered and, as a result, the interference waveform positions following the temperature change shift relative to the positions prior to the temperature change, which changes the intervals between the individual peak positions. The extent by which the peak positions of the interference waveforms change corresponds to the extent of the temperature change. In addition, the distances between the peak positions of the interference waveforms correspond to the distance by which the reference mirror 20 moves. Thus, by accurately measuring the intervals between the peak positions in the interference waveforms based upon the distance by which the reference mirror 20 is displaced, the change in the temperature can be measured.
The temperature of an electrode plate at an upper electrode disposed inside a processing chamber of a substrate processing apparatus, as well as the wafer temperature, can be measured by using the temperature measuring apparatus described above. It will be particularly convenient if the wafer temperature and the temperature of the electrode plate or the like can be measured at once. Namely, by measuring the temperatures of a plurality of temperature measurement targets through a single temperature measurement operation, the labor and the time required for the temperature measurement can be greatly reduced at minimum cost.
However, the following problems may occur if the temperatures of a plurality of measurement targets disposed so as to face opposite each other, such as the wafer and the electrode plate of the upper electrode, are to be measured. For instance, the measurement light originating from the light source may be transmitted via optical fibers by, for instance, installing the optical fiber to be used for the wafer temperature measurement through the bottom part of the processing chamber and installing the optical fiber to be used for the measurement of the temperature at the electrode plate of the upper electrode through the upper portion of the processing chamber. Since this requires the optical fibers to be laid out from the top and the bottom of the processing chamber to transmit the measurement light beams originating from a single light source, the optical fiber layout becomes very complicated, which is bound to complicate the installation process for the temperature measuring apparatus.
As an alternative, both the optical fiber to be used for the wafer temperature measurement and the optical fiber to be used for the measurement of the temperature at the electrode plate of the upper electrode may be disposed through the upper portion of the processing chamber. However, since the wafer is placed below the electrode plate of the upper electrode at a distance from the electrode plate, an insertion hole through which the optical fiber for radiating the measurement light onto the wafer, i.e., one of the measurement targets, is to be inserted, needs to be formed at the other measurement target, i.e., the electrode plate of the upper electrode, in order to enable radiation of the measurement light onto the wafer. This means that it becomes necessary to specially form the hole at the measurement target through an additional process.